We shall investigate the intermediate stages in the in vitro assembly of protein from tobacco mosaic virus. Of specific interest are the details of formation of the nucleus equivalent to about two turns of the virus rod and of the stage requiring the binding of protons. Experimental approaches will involve velocity and equilibrium sedimentation. For the latter, data will be reduced using an original procedure applicable to polymerizing systems. In addition, we will explore the possibility of using protein cross-linking reagents to fix molecular aggregates for their subsequent identification by gel electrophoresis. We have separated by sephadex gel filtration fd bacteriophage A protein and are determining the number per virus particle, preliminary to carrying out its biophysical characterization. In addition, our results on the ion etching of both TMV and T4 bacteriophage suggest that this technique may allow us to determine the location and orientation of the single stranded DNA within fd. Also, we have carried out fluorometric studies on DNA and synthetic polynucleotides stained with quinacrine, to establish whether F bodies observed by fluorescent microscopy in human sperm represent the Y chromosome. Finally, we have performed sedimentation velocity and electron microscopy studies on the DNA isolated from bovine spermatozoa.